Intakes of various water related power plants such as hydroelectric and nuclear electric generating plants, water supply and treatment plants, inboard, outboard or inboard/outboard boat motors, water jet motors, jet ski equipment, submarines, etc. generally operate in large bodies of water such as rivers and lakes. These power plants typically circulate the contents of the body of water about which they are operating in throughout their power mechanisms or engine. Frequently, these bodies of water contain elements that are undesirable to optimum performance of the power plant. For example, the water may contain algae, barnacles and other marine growth. In particular, a very detrimental organism that is increasingly troublesome throughout the world, most recently found in the Great Lakes of the United States, but historically also found in the waters in Central and Eastern Europe, is the Dreissena polymorpha, commonly referred to as a zebra mussel. This fresh water invader and its implications is described in a Cornell University publication, Sea Grant Fact Sheet 11-1989 which is herein incorporated by reference. Copies are available from New York Sea Grant Extension Program, State University College, Brockport, N.Y. 14420.
The zebra mussel is a serious problem because it attaches itself to the interior wall of intake pipes of power plants, boat motors, etc. These intake pipes generally bring cool water from the river into the plants and motors for the purpose of cooling. In the case of boat motors, the water is circulated around the engine to cool it and then ejected back into the river through a separate discharge channel. Colonies of these bivalve mollusks gather in the intake pipes. In fact, they have been known to stack themselves 8" thick or more. Once they are attached, they restrict the flow through the intake pipes, seriously affecting the efficiency and cooling capacity of electric plants and boat motors. In addition, zebra mussel larvae travels up into the intake pump itself, further affecting the cooling capacity. Ultimately, this reduced cooling capacity results in engine failure.
The zebra mussel spreads extremely rapidly to uninfested waters by unknowing fishermen and recreational boaters. The mussels attach themselves to boat hulls and engines, and as the boats travel, the population spreads. Unfortunately, the mussel has no significant predators, so there is no natural population control. Alternately, to exterminate them with known methods would kill most every life form in a given body of water. Therefore, chemical extermination is not an attractive solution to the zebra mussel problem. One option is to introduce a chemical in the area of concern; pipe, intake, etc. and meter the flow. This is viable to protect equipment, but is detrimental to the environment if sufficient quantities are used.
As a minimum control measure, it is desirable to prevent significant population of the mussels attached to places where they can cause the damage described above. A further, more stringent control measure is to prevent the zebra mussels from attaching themselves to these places at all. Namely, anywhere that water is being taken from the river or lake for any reason, it is desirable to prevent mussels form attaching to the transporting hardware. For example, in the case of power plants, the large pipes drawing water from the lake should be kept mussel-free. In the case of boat motors, the cooling water intake should be kept mussel-free. Equivalent examples exist for many other instances where water is drawn from a body of water.
Traditionally, special paints have been used to control the growth of marine life, especially on boat hulls. Bottom anti-fouling paints typically contain heavy concentrations of tin or copper. These paints are relatively effective in controlling the growth of algae, etc. when they are newly applied. Eventually, the paint wears off, contaminating the water, and is of limited effectiveness. For this reason, the boat owner must reapply the paint yearly. One possible solution to the mussel problem would be to plate the interior of all pipes prior to manufacture of a boat motor. Eventually, however, the preventative coat would wear off and the mussels would attach themselves. Another solution would be to make the pipes from copper or tin. While this would last longer, it will still cause hazardous metals to be deposited into the water supply.
Another possible preventative measure would be to place a screen over the intake pipe. This would prevent organisms, including adult mussels, from entering the pipe and attaching to the interior wall. However, the larvae are very small and it would be very difficult to utilize a small enough mesh to exclude the larvae without subsequently affecting the flow rate. Therefore, this is also a very limited solution. Yet another solution is to utilize centrifugal separation, but the larvae density is very close to that of water, and would pass through.